Work and Pensions Secretary David Blunkett has resigned over his links to the private company DNA Bioscience. The BBC News Website looks at the issues involved.

What was David Blunkett's job?

He was brought back into the Cabinet as work and pension secretary after the May 2005 general election. He had previously been forced to resign as home secretary in December 2004, over claims he fast-tracked a visa application for his married lover's former nanny.

Why did he quit this time?

Mr Blunkett handed his resignation to Tony Blair after concluding his position had become "untenable" after breaching the ministerial code of conduct over his business dealings.

What did he do wrong?

After being sacked as home secretary in December 2004 Mr Blunkett took paid work without seeking advice from the Independent Advisory Committee on Business Appointments.

What's wrong with that?

The ministerial code of conduct says that the committee should be consulted before ex-ministers take up any private sector role within two years of leaving office. A succession of Westminster standards watchdogs said he had clearly broken that code.

What did Mr Blunkett say?

He said that with hindsight this had been a mistake, but said he had thought it was voluntary to seek advice. Letters from the committee to Mr Blunkett subsequently published showed he had been reminded three times that the committee should be consulted.

What did Number 10 say?

Tony Blair had been defending Mr Blunkett, saying Mr Blunkett had made a mistake, but that it did not stop him doing his job.

How did Mr Blunkett try to put things right?

He issued a statement on 31 October saying his sons had agreed to sanction the sale of shares he had bought in one of the firms he worked for, DNA Bioscience, to avoid "continuing misinterpretation of the position". A spokesman for his department said he would not be making any profit on the sale. He also stressed he had been transparent about all of his jobs, which are listed in the MPs' register of interests.

What now for Mr Blunkett?

Mr Blunkett returns to the backbenches, to continue serving as Labour MP for Sheffield Brightside.